When you look at the history of the Internet it is the simple standards and protocols that have succeeded. Take SOAP v. REST for example. Amazon supported both standards and the market spoke. About 98% of their transactions were accomplished using the simpler REST protocols. Simple wins. Simple is easier to adopt.

The aim of OAUTH 2.0 is laudable. We absolutely need simple authentication that works pervasively across the Internet. We need portable user authentication. The more complex you make Authentication the less secure it gets.